1. field of the Invention
This invention relates to a method and apparatus for precisely locating a separation split of uniform profile in a rotating stack of flexible storage disks; said split permitting uniform transducing access to otherwise inaccessible disk storage surfaces.
2. Description of the Prior Art
Matter disclosed in related U.S. patents 3,867,723 (Penfold et al) and 3,936,880 (McGinnis et al) cross-referenced above is incorporated herein by following references thereto.
Ventilation of spaced flexible disk surfaces in a multi-disk file -- to stabilize rotation and prevent adhesion between interfacing surfaces -- is known in the art. Ventilation flow may be supplied through radially porous spacers (refer to Penfold et al U.S. Pat. No. 3,867,723 cross-reference No. 1 above) or through aligned off-axis holes in the disks (U.S. Pat. No. 3,509,553 granted April 28, 1970 to Krijnen).
U.S. Pat. 3,936,880 by McGinnis et al (cross-reference No. 2 above) teaches that at certain ventilation pressures the stack can be disturbed from an unsplit configuration into a stable split configuration in which a variably positioned split suitable for random transducing access is sustained autonomously (without i.e. external force). Characteristically this access split also referred to herein as auto-sustaining split and self-sustaining split) has a circumferentially uniform profile which desirably provides uniform transducing access at all radial coordinates (tracks) within a useful radial range.
An important factor in respect to effectively utilizing this technique of forming auto-sustaining splits is to be able to establish the position of the split precisely and quickly at a designated (target) axial position (coordinate) in the stack. The transitional delay in forming such a split is not negligible. Hence any inexactitude in the process employed to establish the position of said split represents a probable cause of error and retrial (requiring erasure of the split and formation of another split at another position). Undesirably this increases the average access delay (seek time) presented to the system user. If the inexactitude cannot be controlled within bounds (i.e. if the probability of error in retrial cannot be made significantly less than the probability of error in the initial access attempt) the increase in the average access delay time is compounded.
A problem in this regard is that for volumetric storage packing efficiency it is desirable to use ultra-thin large diameter disks (e.g. 0.001 inch thickness; 12 inch diameter) which, in the unsplit mode, rotate at closely spaced intervals (e.g. 0.0035 inch). With such parameters slight but unavoidable irregularities in the disk orbits, due to natural centrifugal wobble and run-out (variations in circumferential thickness) tend to significantly degrade the preciseness of interface location.
Even if elaborate and/or fairly expensive (or bulky) sensing apparatus is employed to sense the position of a target interface in the unsplit stack (refer to cross-references 4 and 5 above) the possibility of erroneous positioning of the auto-sustaining split cannot be completely eliminated.